Update rock_pull_request workflow to test against k8s instead of or in addition to microk8s

[shayancanonical]

The rock_pull_request workflow is testing rocks with kgoss in microk8s: https://github.com/canonical/observability/blob/main/.github/workflows/rock-pull-request.yaml#L43

We should switch to k8s. Or at the very least, allow input to configure underlying k8s for the test (allow choice between microk8s or k8s)

Note: to use concierge to prepare a k8s preset, one needs to ensure containerd is completely uninstalled beforehand (https://github.com/canonical/workflows-team/blob/main/.github/workflows/terraform.yaml#L92). Can optionally install a docker snap afterwards if required. Unfortunately, at this time, specifying docker as an extra-snap for concierge prepare fails since the containerd conflict occurs when concierge executes k8s bootstrap - extra-snaps are installed before k8s bootstrap is executed
Reference: https://documentation.ubuntu.com/canonical-kubernetes/release-1.32/snap/reference/troubleshooting/#the-path-required-for-the-containerd-socket-already-exists
Workaround will become obsolete once a strictly confined k8s snap is released